The present invention relates generally to disc drive data storage systems. More particularly, the present invention relates to aligning servo wedges in a disc drive.
A disc drive includes one or more magnetic discs that are capable of storing data. Typically multiple discs are mounted in a disc stack for rotation on a hub or spindle. A typical disc drive also includes one or more transducers supported by a hydrodynamic air bearing which flies above each magnetic disc. The transducers and the hydrodynamic air bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to retrieve information from the magnetic discs and to store information on the magnetic discs. An electromechanical actuator operates within a servo system to move the data head radially over the disc surface for track seek operations and to hold the transducer directly over a track on the disc surface for track following operations.
Information is typically stored on the magnetic discs by providing a write signal to the data head to encode flux reversals on the surface of the magnetic disc representing the data to be stored. In retrieving data from the disc, the drive controller controls the electromechanical actuator so that the data head flies above the magnetic disc, sensing the flux reversals on the magnetic disc, and generating a read signal based on those flux reversals. The read signal is then decoded by the drive controller to recover the data represented by flux reversals stored on a magnetic disc, and consequently represented in the read signal provided by the data head.
Accurate positioning of the data head over a track on the disc is of great importance in writing data to the disc and reading data from the disc.
In prior systems, servo operations were accomplished based on a dedicated servo head. In a dedicated servo type of system, servo information is all written to one dedicated surface of a disc in the disc drive. All of the heads in the disc drive are mechanically coupled to the servo head which is used to access the servo information. Thus, all of the heads in the dedicated servo disc drive are positioned based on the servo information read from the servo surface. This type of system allows the disc drive to conveniently execute parallel read and write operations. In other words, with appropriate circuitry in the drive controller, read and write operations can be executed in parallel using a plurality of the data heads mounted on the actuator, the data heads being simultaneously positioned based on the servo information read from the dedicated servo surface.
However, track densities on magnetic discs have been increasing for many years. Increased track densities on the magnetic disc require more accurate and higher resolution positioning. The mechanical offset between heads in a dedicated servo system can exceed one track width. Thus, the industry has seen a shift to embedded servo information in certain applications.
In an embedded servo system, servo information is embedded on each track on each surface of every disc. Thus, each data head returns a position signal independently of the other data heads. Therefore, the servo actuator is used to position each individual data head while that particular data head is accessing information on the disc surface. The positioning is accomplished using the embedded servo data for the track over which the data head is then flying. Typically, the servo data is written as a plurality of servo wedges that extend radially from the center of the disc to the outer edge of the disc. Typically the servo wedges are equally spaced about the circumference of the disc surface.
In an embedded servo system, operation of the servo system is more efficient when the servo wedges of the various disc surfaces are aligned with each other in relation to the spindle. One existing method of aligning the servo wedges is to write the servo wedges to the entire disc pack in one operation. However, writing the servo wedges to the entire disc pack in one operation typically requires the use of the disc drive""s ball-bearing spindle to rotate the disc stack during the writing of the servo wedges. When the discs are servo-written using the ball-bearing spindle, the ball-bearing spindle motion gets written into the servo wedges. This can result in a significant amount of written-in repeatable run-out in the servo track. To reduce the amount of written-in repeatable run-out in the servo track, the servo wedges can be written to each disc, one at a time, on an air-bearing spindle, which is smoother than the disc drive""s ball-bearing spindle. However, presently there is not an efficient method of aligning the servo wedges when the servo wedges are written to each disc individually.
The present invention provides a solution to this and other problems and offers other advantages over the prior art.
The present invention relates to aligning servo wedges in a disc drive.
One embodiment of the present invention is directed to a method of aligning servo wedges of a plurality of disc surfaces in a disc drive. Pursuant to the method, multiple servo wedges are written, one adjacent another, continuously across an entire circumference of each disc surface. Then one of the disc surfaces is designated the master surface. Every nth servo wedge on the master surface is then designated as a master wedge, where n is a positive integer. Next, the servo wedges on the non-master surfaces which are most closely axially aligned with the master wedges are selected. Then all of the non-selected and non-master wedges are erased.
In one embodiment of the present invention, writing the servo wedges continuously across the entire circumference of the disc involves the following steps. The desired servo sample duration, the desired final servo sample rate and the desired final servo period are determined. Then the maximum number of servo samples of the desired duration that can fit within the desired final servo period is calculated. A variable, n, is used to represent the maximum number of samples. The disc is rotated at the spindle frequency which is to be employed during normal operation of the disc drive. A servo pattern is then written to the disc at a frequency equal to n times the desired final servo sample rate.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.